Power measurements of received signals are important in communication systems. These measurements are used for many purposes, such as determining signal to interference ratios (SIRs), signal to noise ratios (SNRs), power control, and numerous other purposes. Another use of these measurements is for cell search, where a wireless transmit/receive unit (WTRU) selects and synchronizes to a particular cell.
To illustrate using the time division duplex (TDD) mode of the proposed UTRA wideband code division multiple access (W-CDMA) system, in step 1 of cell search, the WTRU measures the power of the primary synchronization signal. In step 2, the WTRU measures the power of secondary synchronization channels and in step 3, the WTRU measures the power of the midamble sequence of the broadcast channel (BCH). Inaccurate power measurements during cell search could lead to the WTRU selecting a non-optimal cell or possibly an unsuccessful cell synchronization. For these purposes, it is important to use accurate measurements of the received signal power.
In code division multiple access (CDMA) communication systems, a particular received signal's power level is typically determined by correlating a received vector with a code of the particular signal. The received vector contains all of the signals transmitted over the particular signal's spectrum along with noise. Since correlating the particular signal's code with noise alone results in some small correlation, it is desirable to remove the noise component from the correlated signal. To remove the noise, correlated samples below a predetermined threshold value are discarded as being noise and are not included in the received signal power determination. Although this approach improves the accuracy of the received signal power determination, it is desirable to increase the accuracy further.